It's so easy for enthusiasts to get excited about horsepower numbers, rpm levels, and sound, while skipping some very key factors of a well-designed engine. Some build requests are realistic while others are not even close. And it's actually just as important for the engine builder to clarify the needs of the customer, as a totally mismatched engine can easily be an embarrassment to the builder and to the driver/owner.
This "Power Principles" series will focus on how you, the engine buyer or home builder, can better assess your needs and compare them against your wants. Yes, we have needs. Yes, we have wants. Yes, there are sometimes ways to meet in the middle. As we cover some different scenarios and viewpoints, keep your mind focused on one statement: Build the engine for the application. Don't make the application fit the engine. This will help you get the engine that you need and it will also help your engine builder's (or your) reputation stay in the clouds. We all like win/win situations, right?
To get an idea of what you want in an engine, here are some key questions that the average engine builder will ask of a potential customer:
1. What kind of vehicle do you have?
2. Is this a street, street/strip, or race application?
3. Do you have a horsepower number in mind?
4. If you could pick where the horsepower would peak, where would it be?
As we discuss the different varieties of applications and try to focus on the associated implications, try to answer these questions as honestly and realistically as you can so that you can better clarify your own needs.
Vehicle Specifications
Regardless of what your horsepower desires may be, almost everything depends on what type of vehicle the engine is going into, as vehicle weight plays a huge role in how the engine will work within its confines. A very heavy car or truck requires far more torque to get it moving than a light one will. In most cases, it's best to pair a heavy vehicle up with a milder cam and an engine that has a horsepower/torque curve geared more toward getting (and keeping) a heavy vehicle moving. A very light car, by contrast, can get away with a lot more in terms of how "peaky" an engine is. The torque curve doesn't need to be so high or so broad, and the horsepower curve can be shifted to the right to gain more power at peak rpm.
Let's think about some extreme examples to demonstrate this.
You're looking to build an engine for your '77 Ford Thunderbird. (Don't laugh, it happens). This car has a curb weight of 4,808 pounds (Stop laughing). Now, as a means of demonstrating our point, would it be prudent to stick a 7,500-rpm 347 in this car?
On the flip side, you're looking to build an engine for your Cobra replica. At around 2,500 pounds, it's not necessary to design an engine with a flat line torque curve (although there really are no downsides to doing so) because it takes much less torque to move such a light car from a dead stop. You would be able to get away with a little more cam, a little larger cylinder head port volume, quicker ignition timing curves, and, ultimately, steeper horsepower/torque curves that maximize horsepower. It's just a lot easier to get 2,500 pounds moving than 4,800 pounds.
Application
The mode of operation (how you drive it) goes hand-in-hand with the vehicle type. A street-oriented vehicle, which the majority of readers probably have, needs to have more of a focus on driveability, lower maintenance, and just less drama in general. It's very easy to get carried away with large camshafts and large cylinder head volumes, but these items don't always lend themselves to trouble-free operation. Street cars spend a lot of time at cruising rpm. That larger cam with the cool, lopey idle can cause bucking while cruising, and if you've ever experienced this, it doesn't make for a fun cruising experience. You'll find yourself grabbing the next lower gear or speeding up to get the engine running at a higher rpm.
This is where horsepower and torque curves come into play. The horsepower curve and the torque curve define how an engine will operate in its environment, and camshaft design has a direct impact on the curves.
For street cams, lower duration numbers will help keep the horsepower curve shifted toward the left side of the graph, single- pattern profiles help cut down on overlap and the possibility of reversion, and wider LSAs will help with idle characteristics, engine vacuum, and broader torque curves. Does this mean that you will have a weak engine because the cam is smaller? Of course not. Building an engine with a focus on the intended purpose can often make a car feel and run quicker, big cam or not.
It's very hard to have your cake and eat it too when dealing with operating curves. If you prefer the rev-happy engines, then you have to be prepared to have a softer bottom end. If you prefer the low-rpm torque monsters, then you have to be prepared for the engine to run out of breath at a lower rpm ceiling.
For illustration purposes, look at these two horsepower/torque graphs:
As you can see, the higher that you move the horsepower peak, the less average horsepower and torque you get. The curves actually take more of a linear shape instead of producing a "fuller" curve shape. Without the low-rpm torque, a heavy car would feel slow and sluggish. You can also see on the graph that represents the "fuller" curves, the horsepower starts to drop off at a lower rpm. In the same manner, you can see how this situation wouldn't be beneficial for a race-oriented engine that needs to rev and make horsepower up higher. Both scenarios have their places. There's nothing wrong with either one of them as long as the engine fits the application.
Horsepower Goals
We all want big numbers. Big numbers sell engines. Big numbers are bragging rights. For those reasons, it's very hard to get people to focus on the application instead of the numbers. However, this is one of the criteria that many builders use to qualify the customers and set them up with the correct powerplant. Again it's easier to talk in extremes sometimes, so we'll offer one "extreme" example.
"I want an engine for my super-fly '77 Ford Thunderbird. It's a car that I'll be driving almost every day, back and forth to work. It's got the factory 302 and 3.00:1 rearend in it, and I'm wanting something around the 600hp range."
OK, let's use some of our theory in practice. This is a very heavy car, with the intended purpose of driving in a daily commute. Not a race car, not a street/strip car, but a street car in every sense of the wordùair conditioning, fuzzy dice, the whole nine yards. Now, there's nothing inherently wrong with wanting 600 horsepower, but 600 streetable horsepower from a 302 is pretty unrealistic. Even getting 600 hp from a naturally-aspirated 347 would take some very keen engine building skills, high-compression ratios, big cylinder heads, and a nicely sized camshaft. Now, if the customer would be open to going with another engine platform, such as a stroked big-block, or even a moderately sized small-block with forced induction, reality looms a little closer. What's our motto? Build the engine for the application.
We haven't reiterated the "wants versus needs" argument lately, but this would be a great time to do so. We have wants. We have needs. Sometimes we need to compromise and it's very often that our needs are of more importance than our wants. Our Thunderbird would be one of those cases. Yes, it would be nice to have 500-600 hp, but the customer needs torque, throttle response, and a usable powerband. They don't always realize that or what it means until they drop a high-strung small-block between the framerails and wonder why it is sluggish.
Fitting In With The Crowd
So you've figured out what type of car you have, what it weighs, and what engine combination would give you the optimum performance given your application. The next thing to consider is whether or not this combination is a direct replacement or bolt-on proposition, or if it requires further modifications to employ it. Stroking your present block, or one of similar dimensions, offers the least amount of drama from an installation standpoint, however, the increased cubic displacement will no doubt require a larger exhaust system (or at the vey least, headers), a higher-flowing intake manifold, cylinder heads, carburetor or EFI components.
Things get really complicated when you decide to change engine families altogether, as you now have to factor in accessory drive systems, hood and fender clearance, and weight balance to name a few things. Improved power output can also require a heavier-duty clutch or automatic transmission, a higher stall-speed torque converter, and even suspension changes including components and settings. This is where research on your behalf will pay off. Your engine builder probably has some experience with various combinations, and may be able to offer you some fitment advice, but you'll want to seek out others who have made similar modifications, and question them regarding many of the considerations that we've mentioned here.
Ford Windsor Small-Block
The Ford small-block has been a staple of Blue Oval hot-rodders for years. Starting with the 221ci V-8 in 1962-1963, things soon blossomed for the small-block, with the bore and stroke increasing to provide displacements of 260, 289, 302, and 351 ci (with the larger 351W block). Various versions of these engines found themselves in a huge amount of Ford/Lincoln/Mercury vehicles, and the 302 helped keep Ford running in the '80s and '90s with the 5.0L in the Fox-body Mustangs.
The Ford small-block has been a staple of Blue
The 302 and 351 are the most common blocks used for performance applications, with the 302 giving rise to 331- and 347ci stroker kits. Stroker kits for the 351W block can produce cubic inches in the 430-plus range. Adding to that is a plethora of aftermarket parts including cylinder heads, camshafts, rotating assemblies, and a vast selection of accessories. Although no longer available in factory vehicles, various manufacturers such as Dart, World, Ford Racing, and more, are producing aftermarket 302/351 blocks capable of supporting more than 1,000 horsepower.
Ford Cleveland Small-Block
Manufactured from 1970-1974, the 351C was available in several different vehicles, including the Ford Mustang and Torino, Mercury Montego, and Mercury Cougar. With the cylinder heads being offered in several different flavors, engines were offered to produce lower-end performance and screaming high-end performance as well. The 9.200-inch deck height block combined with the 4V canted heads soon found its way into stock car racing, and became the basis for lots of engine and cylinder head designs from then on out. The aftermarket is also kind to the Cleveland family, with many companies producing aluminum cylinder heads (Edelbrock, Trick Flow, CHI, AFD, and more), long stroke rotating assemblies, and the usual selection of camshafts, intakes, and other parts available to other Ford engine families.
Ford FE
You can't have a sentence with both "Ford" and "performance" in it without the FE engine coming to mind. The FE engine is the epitome of older big-block muscle car powerplants. What Ford fan hasn't heard of the 427 "side oiler" or the 428 "Cobra Jet"? The Shelby Cobra and Ford Mustang crowds pushed these engines into infamy, not to mention the Ford Thunderbolts, Galaxies, and Fairlanes that proved their performance at the local dragstrips. Let's not leave out the Mercury guys with the big-block Cyclones and Cougars.
The performance market boomed for the FE in the '60s/'70s and starting with a 352 or 390 block, you could easily bolt on some parts and have a barnstormer of a powerplant. Even with factory pieces, displacements of 454 cubic inches were possible by combining the large bore of the 427 block with the long stroke of the 428 crankshaft. Low riser, medium riser, high riser, tunnel port, and even overhead camshaft (SOHC, aka "Cammer") heads were options.
So what's the easiest way of snagging an FE today? Check the junkyard and salvage yards for blocks from pickup trucks and passenger cars. They're still out there in fairly large quantities. Combining a 390 block with a Scat 4.250-inch-stroke crankshaft can net you 445 cubes and there are even longer stroke crankshafts available. Companies like Shelby, Genesis, and Robert Pond are offering brand-new FE blocks in your choice of cast-iron and aluminum--prices are at the higher end, compared to other Ford powerplants. Displacements of 527-and-up are possible. Want a 700hp FE for your Cobra replica? Not a problem. Several cylinder head and intake manufacturers have stepped up to the plate to provide superior induction. FEs have made a comeback and they're just getting started.
Ford 385 Series (BBF)
The other big-block Ford is the 385 series, or what we commonly see manifested as the 429 and 460 engines. The 385 series was the successor to the Ford FE big-block. Remember the Boss 429? Yep, that's a 385 series engine. Ford really outdid itself when it introduced this engine family. Offered with a 4.360-inch bore and either a 3.590-inch (429) or a 3.850-inch (460) stroke, these engines were just itching to make some horsepower. Unfortunately, the 460 days came right before and during the '70s gas crunches, when economy was king. Low compression ratios and severely retarded cam timing made these engines dogs in the vehicles they were placed in (Galaxie 500s, Lincolns, Thunderbirds, and more).
The gas crunch slowly went away, and many new performance parts started worming their way into the aftermarket. Crate engines, stroker kits, cylinder heads, camshafts, and more all became commonplace. Want a 604ci BBF? Not a problem. Aftermarket blocks are out there with 4.600-inch bores and stroker crankshafts are floating around everywhere. Even the Boss 9 has made its comeback with the availability of Jon Kaase's "new" Boss 9 cylinder heads.
When it comes to horsepower, the sky's the limit with the 429/460-based engines. Factory blocks will handle huge amounts of power and new blocks from Ford Racing (and others) will allow power numbers up into the "thousands."
Modular Engines
While we could easily include the turbocharged 2.3-liter four-cylinders, inline sixes, and V-6 engines in this story, they just don't seem to be very popular when there are so many good V-8 candidates. What has become popular are the Ford modular engines from the '96-and-newer Mustangs. This includes the Two-Valve and Four-Valve 4.6L and 5.4L engines, as well as the new-for-2011 5.0L Coyote engine.
In naturally-aspirated form, the only decent performance modulars are the DOHC 4.6L and 5.0L engines, offering 305 hp and 412 hp respectively. The supercharged 5.4L from the GT500 is also a hot commodity making more than 500 hp. All modular engines benefit from a rich aftermarket thanks to the late-model Mustangs, and offer just about unlimited engine power with great driveability.
While the Two- and Four-Valve 4.6L engines can be had used and quite inexpensively, we'd put our money on the new 5.0L Ti-VCT DOHC crate engine from Ford Racing Performance Parts. It's the same engine that powers '11-and-newer Mustangs, and offers 412hp and 390 lb-ft of torque. Parts are continually coming out for this engine, and a well-tuned version with bolt-on performance parts can easily exceed 400 rwhp, with super- or turbo-charged versions making well over 500 rwhp--and the engine can handle it with ease. We expect to see the new 5.0L crate engine from Ford Racing Performance Parts become vastly more popular than the current modular crop of engines.
While the Two- and Four-Valve 4.6L engines can be had used and quite inexpensively, we'd put our money on the new 5.0L TI-VCT DOHC crate engine from Ford Racing Performance Parts
Conclusion
There are so many different variables to take into consideration when planning out an engine build, and it's almost impossible to address every single one. We haven't even covered your budget in all of this, which oftentimes is either the first question to answer or the last. Building an engine can be a daunting task, but if you think your way through it, you can have a complete combination that will make you happy when cruising, and will make you grin when you mash the gas.
Now it's time to be honest, think about what your goals are, and do a little research on the pros/cons of your engine plan. Check back next month, as we hop along to the next step, which is exploring the foundation of the engine: the block. We will explore the different options that Ford enthusiasts have, and even cover some different machining techniques and engine building practices. Following that article, we'll cover how to properly choose the correct cylinder heads, cam, and intake for your combination in the third installment of our "Power Principles" series.